I can imagine airliners have their entire maintenance "street" completely tailored to maintain their Boeing aircraft, so unless you already happen to have Airbus, a switch is not likely it seems. Can anyone shed some light on that?
What's certain is that all airlines dream of having only one manufacturer. If they have multiple, they often try to make one hub service one type of plane, e.g. fly all their Airbuses past one airport and all their Boeings past another (For competing models such as A320 vs 737)
A good idea even when all planes are the same manufacturer is probably to not have all planes being the same model so they all get grounded in case of a discovery (An NG 737 is not the same as an older one which is not the same as a MAX etc)